A Novel Pathosystem With the Model Plant Arabidopsis thaliana for Defining the Molecular Basis of Taphrina Infections

Plant-associated yeasts modulate host immunity to promote or prevent disease. Mechanisms of yeast perception by the plantinnate immune system remain unknown, with progress hindered by lack of a model system with the model plant Arabidopsisthaliana (Arabidopsis). A yeast strain of Taphrina tormentillae, named M11, was previously isolated from wild Arabidopsis.Taphrina have been found on many non-host plants, and their complex ecology remains understudied. Here, the interaction ofM11 with Arabidopsis was characterised. Infection of Arabidopsis with the birch pathogen T. betulina, used as a non-host con-trol, triggered typical defence activation features but did not multiply, demonstrating Arabidopsis had immunity against a non-adapted yeast. M11 triggered attenuated defence activation features, grew in planta, and caused subtle but clear leaf deformationsymptoms, demonstrating it is pathogenic. M11 was widely distributed in environmental sequencing data and found on multi-ple non-host plants, suggesting Taphrina play previously unrecognised ecological roles on multiple plant species. M11 genomefeatures involved in host interaction were analysed, and potential immune stimulatory molecules in chitin-free cell walls wereidentified. A pilot screen demonstrated the utility of reverse genetics with Arabidopsis and identified that the BAK1 co-receptoris involved in the perception of M11 Taphrina cell walls